1. Field of the Invention
The present invention relates to a semiconductor device and a semiconductor device casing.
2. Description of the Background Art
A power semiconductor module in which one or two or more power semiconductor elements (semiconductor chips) are included in a casing and the inside of the casing is sealed with a sealing material has been known as a semiconductor device. Bonding wires etc. made of aluminum are used for these power semiconductor elements in order to electrically connect the semiconductor chips mounted on an insulating substrate to an electric circuit or terminals formed in the insulating substrate.
The sealing material inside the casing is composed of an epoxy resin etc. and serves for protecting and insulating the semiconductor chips, the bonding wires, etc. which are received in the casing. To this end, in the power semiconductor module, the sealing material is charged into the casing to reach a height at which the bonding wires inside the casing can be sufficiently covered and insulated. On the other hand, there is a request for reduction of the size and thickness of the power semiconductor module, and it is desirable that the height of the casing is also made low as long as there is no problem. When the sealing material which is liquefied is injected into the casing, the sealing material is injected up to the vicinity of an upper surface of the casing so that the insulation property inside the casing can be achieved by the sealing material in balance with the reduction of the size and thickness.
Since the sealing material is injected up to the vicinity of an upper edge of the casing, the sealing material may run onto the upper surface of the casing during the injection. In addition, the sealing material may run onto the upper surface of the casing during conveyance before the injected sealing material is solidified.
The sealing material running on the upper surface of the casing may cause poor external appearance of the power semiconductor module. When the casing is covered with a cover and adhesively fixed to the cover, the sealing material running on the upper surface of the casing may lower the adhesion because the upper surface which is the bonded surface of the casing is not flat.
Provision of a flange in an inner surface of the casing (JP-A-8-130291) or provision of a step portion in an inner surface of the casing (JP-A-4-354354) has been proposed for preventing the sealing material from running on the upper surface of the casing.
However, the flange or the step portion provided in the inner surface of the casing is formed to face toward the inside of the casing so that the sealing material can be prevented from reaching the upper surface of the casing. Thus, the injection amount of the sealing material is limited up to a height where the flange or the step portion is formed. Therefore, the flange or the step portion cannot satisfactorily meet the request to inject the sealing material up to a position as close to the upper surface of the casing as possible in order to enhance the insulation property. Even when the sealing material can be injected up to the vicinity of the upper surface of the casing, it is difficult to prevent the sealing material from running on the upper surface of the casing.